This invention is directed generally to enclosures or housings for electrical or electronic apparatus and more particularly to the provision of a novel housing or enclosure which provides EMI and RFI shielding.
The problem of electromagnetic interference (EMI) and/or radio frequency interference (RFI) is well-known in the electrical and electronic arts. In this regard, many electrical and/or electronic components and/or circuits may be adversely affected by such types of interference signals. Accordingly, it is desirable to provide suitable shielding against such interference for these components and circuits. Additionally, FCC regulations, as well as other practical considerations, require that emissions of such EMI or RFI signals from various circuits and components be held below defined levels. This is to avoid interference with radio reception, or with other such interference signal-sensitive circuits and components.
The prior art has provided a number of enclosures or housings designed for shielding or screening such EMI/RFI signals. Various prior art arrangements of this type are shown, for example, in U.S. Pat. Nos. 2,219,941; 2,876,275; 3,234,318; 4,110,552 and 4,218,578. While the prior art has thus provided a number of housings or enclosures directed to the solution of this problem, there remains room for further improvement.
For example, many prior art devices consist simply of boxes or enclosures made of conductive metallic materials. However, such metallic boxes are not suitable in applications where insulated or non-conductive outer surfaces of the enclosure are required. In such situations, a second or outer housing or an additional layer of a suitable non-conductive or insulating material may be required at additional expense.
Various copper or other conductive foil-like materials have also been utilized inside or outside of such housings. However, such foil materials are very expensive to provide. In this regard, conductive coatings of metallizing materials or foils on desired surfaces of the housings or enclosures may be utilized. However, these designs have heretofore required interconnection with various spring contacts, conductive rubber or metal scraps, wires, screws and nuts, conductive epoxys or the like.
In this latter regard, reliable EMI/RFI shieldings requires that a substantially continuous and unbroken conductive surface be provided, that is that substantially no gaps exist in this surface. This presents particular problems where several components, such as covers or the like, of such enclosures must be fitted together. Additionally, it is often desirable to enclose the electrical circuits or other elements contained in the housing in a suitable potting compound. To this end, a number of relatively large openings may be required for the ingress of the potting compound, requiring later closing of these openings to maintain proper shielding. Mounting or soldering additional shielding material can be both difficult and expensive in such situations.